<!-- 链接的class 是bc-nav,当前页是bc-nav-now  
    样式在default_style.css中 -->
<div class="breadcrumb-nav">
    /
    <a href="main_page.html" style="text-decoration: none  ;"><span class="bc-nav" >首页</span></a>
    /
    <span class="bc-nav-now">公告栏</span>
    
</div>